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Prove that cos10° cos 30° cos 50° cos 70°
16
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hope this helps you my dear
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Answer:
cos30.(cos50cos10).cos70
= root3/2.1/2(2cos10cos50)cos70 root3/2.1/2 (cos60 + cos40 ).cos70.. .[ bcoz 2cosxcosy
= cos(x+y) + cos(x-y)] %D %3D
= root3/4 (cos60.cos70 + cos40cos70)
= root3/8 [ cos70 + 2cos40cos70] %3D root3/8 [ cos70 + cos110 + cos30] %3D
= root3/8 [ cos70 - cos70 + root3/2] %3D root3/8. root3/2 %3D
= 3/16
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